To get things straight.
1: No guild names do not change to null like character names.
2: Character name changes to null are not character based but account based. If you do not log on 1 character for a year but you do log onto other characters on that account , none of your character names will be changed to null.
3: The actual changing to null is an database script, I'm not sure if this can be done to guilds as well because I'm not sure how their IDs work and how they are connected to their guildleader or guildmembers in the database.. I'm afraid this would require quite some scripting work if it would be possible at all.
4: I'm not moving this topic again but in my opinion he's asking a question, not properly suggesting something, hence why it should not belong in the suggestion section. He's asking if something would be possible, he's not asking for something to be changed.